Technical Field
The present invention relates to a silicon carbide semiconductor device having polysilicon electrodes and a method of manufacturing the same.
Background Art
There are various types of silicon carbide semiconductor devices, such as planar MOSFET (metal oxide semiconductor field effect transistor) devices, trench MOSFET devices, IGBT (insulated gate bipolar transistor) devices, insulated gate thyristor devices, etc., and these have a structure constituted by a gate insulating film, polysilicon electrodes, interlayer insulating film, and aluminum wiring on top of the device. The demand level for dielectric strength, ampacity, and the like in these silicon carbide semiconductor devices is markedly higher than ever before, and improving the breakdown voltage of the interlayer insulating film is a significant problem.
In order to improve the breakdown voltage of the interlayer insulating film, it is necessary to further improve the step coverage characteristics of the interlayer insulating film. As shown in FIG. 5A, if plasma CVD (chemical vapor deposition) is used to form the interlayer insulating film, for example, the interlayer insulating film 4 overhangs along the periphery of the polysilicon electrode 3, forming a “V” shaped depression. As shown in FIG. 5B, if an aluminum contact layer 5 is formed on top of this, an acute-angled aluminum coating is formed in the step, which degrades dielectric strength due to electric fields concentrating there, and does not satisfy demand levels.
As a countermeasure, Patent Document 1 discloses a method whereby the coverage shape of the step is smoothed via reflow processing for 20 minutes at 930° C. after a BPSG (borophosphosilicate glass) film is formed by plasma CVD.
In addition, Patent Document 2 discloses a method whereby isotropic etching such as chemical dry etching is performed while the temperature of the silicon substrate is maintained at 50° C. to 100° C. in order to cause the side face of the polysilicon electrode to incline at an angle of 41° to 65°.